1. Field of the Invention
The invention relates to integrated semiconductor circuits and somewhat more particularly to such semiconductor circuits having at least one bipolar transistor and at least one MOS transistor on a chip wherein contacts from a metal interconnect level to diffused active regions of the bipolar transistor occur over additionally generated interconnects and a method of producing such circuits.
2. Prior Art
Integrated semiconductor circuits with bipolar transistors and MOS field effect transistors on a chip, as well as some of their potential applications, are described in an article by Russell and Frederiksen, Electronics, (June 8, 1978) pages 113-117 and in an insert report by L. Mattera, page 114.
The smallest possible dimensions of bipolar transistors are determined by the relatively coarse metallization grid utilized because contacts, both to the emitter and collector zones, as well as to a base zone, must be produced from this metal interconnect level.
There have been many attempts to alleviate the wiring or interconnect problem by means of, for example, a polysilicon wiring, as described in an article by D. D. Tang et al appearing in IEEE Transactions On Electron Devices, Vol. ED-27, No. 8, (August 1980) pages 1379-1384 or by means of a polycide wiring, as described in an article by Y. Sasaki et al appearing in IEEE Transactions On Electron Devices, Vol. ED-27, No. 8, (August 1980) pages 1385-1389. However, polysilicon interconnects are relatively high-resistant and result in high intermediate resistances. Since the emitter is generally diffused out of the polysilicon in this procedure and because the n.sup.+ and p.sup.+ dopants diffuse into one another, a high emitter/base capacitance also occurs and vitiates the limiting frequency. The use of a wiring composed of molybdenum silicide, as suggested in the earlier referenced Sasaki et al article, does indeed considerably reduce the wiring resistance in comparison to that of a polysilicon wiring; however, the process of producing this type of wiring is very mask-intensive.